Screw.



c. L. CHRISTOFFERSON.

SCREW.

APPLICATION FILED JUNE 5.1916.

Patented Aug. 28, 1917.

CHARLES L. GHRISTOFFERSON, OF WAUKEGAN, ILLINOIS.

SCREW.

Specification of Letters Patent.

Patented Aug. 28, 1911?.

Application filed June 6, 1916. Serial No. 102,010.

To all whom it may concern:

Be it known that I, CHARLES L. CHRIS- TOFFERSON, a citizen of the UnitedStates, residing at Waukegan, Illinois, have invented certain new anduseful Improvements in Screws, of which the following is aspecification.

This invention relates to wood screws and more particularly to that typewhich are designed to be self-countersinking. Ordinarily screws of thistype present numerous disadvantages, one of which is the liability ofthe throats of the cutters to become clogged with the wood shavingsremoved by the cutter. It is one aim of the present invention, therefore, to provide the head of a screw of this type with cutters soconstructed and arranged that the material removed by the cutters mayreadily pass out through the throats provided for this purpose, therebypermitting of the screw being continuously threaded forwardly when beingscrewed into place and obviating the necessity of turning the screw backone or more times in order to remove the material which has lodged inthe throats.

Another disadvantage usually presented by screws of this type is thatthe cutters are so constructed that the wood near the surface is liableto be splintered, thereby marring the appearance of the surface andrequiring the use of wood filler. The invention, therefore, has as afurther aim to so construct the cutters that the wood will be out insuch a manner as to entirely obviate the splintering of the same so thatthe surface of the wood will remain intact.

Ordinarily screws of this type present the further disadvantage that thecutters and associated throats are so formed as to weaken the head ofthe screw so that if considerable force is required in driving thescrew, one side of the head is liable to be broken off. Therefore, theinvention aims further to so form the cutters and associated throatsthat the head of the screw will not be materially weakened.

A further aim of the invention is to provide a screw of this type whichmay be cast or otherwise manufactured at practically the same cost asthe ordinary Wood screw although of such form as to beself-countersinking.

In the accompanying drawings:

Figure 1 is a plan view of the head of a screw constructed in accordancewith the present invention.

Fig. 2 is a bottom plan view of the said head, the shank of the screwbeing shown in section.

Fig. 3 is a detail side elevation of the head end of the screw.

Fig. 4C is a vertical transverse sectional view through the head end ofthe screw.

In the drawings the shank of the screw is indicated by the numeral 1 andis threaded in the usual manner as indicated at 2. The head of the screwis indicated in general by the numeral 3 and is provided with the usualtransverse groove 4 to receive the bit of a screw driver. As isordinarily the case in screws of this type the upper face of the head isflat and the head is of inverted frusto-conical form.

In order that the material removed by the cutters, which cutters will bepresently more specifically described, may be conducted away from thecountersink as the countersink is formed, the conical surface of thescrew head is formed with throats indi cated in general by the numeral5. Each of the throats 5 is preferably of the same width throughout itslength and has parallel side walls and a concave inner or bottom wall 6to permit of more ready clearance of the material passing through thethroat and by reference to Figs. 1, 2 and 3 of the draw ings it will beobserved that the throats are inclined, the upper end of the throatsbeing located at diametrically opposite points with relation to thecircle described by the upper face of the head and at pointsperipherally midway between the ends of the groove 4 in the said head,the lower ends of the throats being also located at diametricallyopposite points. It will further be observed by reference to Figs. 2 andl of the drawings that the throats are gradually decreased in depth fromtheir upper to their lower ends so as to further provide against chokingof the throats. The outer edge of the rear wall of each throat in thedirection of rotation of the screw when being threaded into the materialis sharpened to form a cutting edge and is indicated by the numeral 7,this edge being continuous or unbroken so as to act upon the materialwith a paring cut.

The present invention contemplates further so forming the head that thematerial will first be cut into slivers which are subsequently paredfrom the material as the countersink is formed, through the action ofthe paring edges or cutters 7 and 111 011161 that the material may beslivered as stated,

the conical surface 3 of the head is formed with two sets of sliveringblades 8 which extend spirally along the said surface. The blades 8 ofeach set have their upper or rear ends terminating at that wall of thethroat 5 opposite the wall the edge of which constitutes the paring edge7, and the blades extend, as stated, spirally, and downwardly from theirsaid ends and have their opposite or forward ends merging into thesurface of the said head 3. In other words,the blades of each set extendaround the conical surface of the head of the screw from the relatedthroat 5 approximately three-fourths of the distance between this throatand the other throat 5. Furthermore, it will be observed by reference toFigs. 2 and a of the drawings that the blades 8 gradually merge at theirforward ends into the conical surface of the head 3 so that they maygradually enter the material in order to cut the material into slivers,which slivers as they are out are received between the blades of eachset and are subsequently pared by the edge 7 of the respective throat 5and as they are so pared and severed are allowed to pass upwardly andout through the upper ends of the throats.

In order that the paring edges 7 may the more effectually perform theirfunction the side walls of the throats 5 while being parallel to eachother as above explained, are not disposed in such manner that the edgesof the said side walls which are presented at the face of the head 3 areat right angles to the longitudinal median line of the groove 4, but, onthe other hand, the said side walls of the throats are not only inclinedbut are disposed at an angle to the planes of the side walls of the saidgroove L.

It will be observed by reference to Figs. 2, 3 and 4 of the drawingsthat the sliver cutting blades 8 are spaced apart so that there areprovided relatively wide valleys 9 lying between the said blades, thevalleys being increased in width gradually in the direction of the minoror merging ends of the said blades and these valleys permitting of theready discharge of the slivers which are cut by the said blades. Inorder that the head of the screw may readily enter the wood as the screwis driven into the wood and the wood is cut away by the sliver cuttingblades and paring blades of the said head, there is provided a pair ofdownwardly projecting blades indicated by the numeral 10, these bladesextending circumferentially of the under side of the head the outer edgethereof and each extending from one of the throats 5, a suitabledistance in the direction stated. It will be understood that inasmuch asthe cutting edges of the blades 10 are presented downwardly, theseblades will cut into the surface of the wood and the slivers cut therebywill be removed by a paring edge 11 formed at thesaid side of therespective throat. Thus splintering of the wood at its surface isprevented and the screw head is caused to closely fit within the openingor countersink cut by the said head of the screw. The paring edge 11 isformed by providing the flat upper surface of the head of the screw witha beveled or inclined surface 12, as clearly shown in Figs. 1 and l ofthe drawings.

Having thus described the invention, what is claimed as new is:

1. A screw having its head formed with a chip throat and provided at oneside of the throat with a paring cutting edge and at the other side ofthe throat with sliver cutting means. g i

2. A screw having its head formed with a conical under surface, the saidsurface being formed with a chip throat and being provided at one sideof the throat with a paring cutting edge, the surface at the other sideof the throat being provided with a plurality of sliver cutting bladesextending spirally head, and merging into the said surface of the headat their ends remote from the throat.

4:. A screw having a conical head formed with an inclined chip throatgradually increasing in depth in the direction of its outlet upper end,the outer edge of one side wall of the throat constituting a paringcutting edge and the head being formed with a plurality of slivercutting blades extending from the opposite side wall of the throat nesubstantially circumferentially of the 5. A screw having its head formedwith an inclined chip throat and provided at one side of the throat witha paring cutting edge, the head being formed with substantiallydirection of their ends Which are presented in the direction of rotationof the screw the said head being further provided with a dependingcirculnscribing cutting blade having a downwardly presented cuttingedge.

In testimony whereof I afiix my signature.

CHAS. L. CHRISTOFFERSON. [1,. 2.]

spirally extending sliver cutting blades, the paring edge and thecutting edges of the sliver blades being located within the bounds ofthe conical surface of the head, the sliver 5 cutting blades extendingfrom the last-mentioned side of the throat part-Way around the said headand decreasing in depth in the Copies of this patent may be obtained forfive cents each, by addressing the Commissioner of Patents, Washington,D. G.

